3DPAFIPN as a halogenated dicyanobenzene-based photosensitizer catalyzed gram-scale photosynthesis of pyrano[2,3-d]pyrimidine scaffolds

Utilizing the Knoevenagel–Michael tandem cyclocondensation reaction of barbituric acid/1,3-dimethylbarbituric acid, malononitrile, and aryl aldehydes, a sustainable methodology for the photosynthesis of pyrano[2,3-d]pyrimidine scaffolds has been devised. The present study expounds on the development of a green radical synthetic approach toward this class of compounds. In this study, a novel halogenated dicyanobenzene-based photosensitizer was utilized in an aqueous solution, exposed to air at room temperature, and activated by a blue LED as a renewable energy source for the purpose of generating energy. The primary aim of this endeavor is to employ a recently developed, easily obtainable, and affordably priced halogenated cyanoarene-based donor–acceptor (D–A). The 3DPAFIPN [2,4,6-tris(diphenylamino)-5-fluoroisophthalonitrile]} photocatalyst, as a thermally activated delayed fluorescence (TADF), is capable of inducing single electron transfer (SET) upon irradiation with visible light, thereby offering a facile and efficient approach with a high degree of effectiveness, energy efficiency, and eco-friendliness. The aforementioned phenomenon facilitates the exploration of the temporal changes that have occurred in the interactions between the surroundings and chemical constituents. The present study aimed to investigate the turnover number (TON) and turnover frequency (TOF) for pyrano[2,3-d]pyrimidine scaffolds. Additionally, it has been demonstrated that gram-scale cyclization is a viable method for utilization in industrial applications.


Control experiments on the 4b synthesis
Between benzaldehyde, malononitrile, and barbituric acid, Figure S1 explain the many strategies that have been employed in order to ascertain the necessity of the visible light source and the photocatalyst to reach the activation phase. Experimental investigations utilizing intermediate substances without a photocatalyst were carried out as a control. When the steps of the process involved the reaction of barbituric acid, benzaldehyde, and malononitrile, it was found that 4b of product was only produced in negligible amounts when carried out at room temperature or in H2O reflux conditions without the presence of blue light/3DPAFIPN, as shown in Figure S1: I and II. In the reaction involving barbituric acid, benzaldehyde, and malononitrile, as shown in Figure S1: III, 21% of 4b of the chemical was generated when exposed to blue light, H2O, and at room temperature without 3DPAFIPN. A trace amount of 4b of product was also formed in the reaction of barbituric acid, benzaldehyde, and malononitrile in H2O solution employing the photocatalyst; 3DPAFIPN without the use of blue light (Figure S1: IV).  Figure S1. Control experiments on the 4b synthesis.

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Experiments with the intermediate were conducted to offer additional experimental data for control objectives. The Knoevenagel-Michael cyclic condensation reaction's mechanism can be characterized as a procedure involving the successive occurrence of two different steps.
Arylidenemalononitrile (A) is created in the first step, and then the product is condensed with barbituric acid (3) in the second. Using a 3DPAFIPN and H2O solution, benzaldehyde (1b) and malononitrile (2) were agitated by exposure to visible light. The intermediate (A) was found in 92% of cases, as shown in Figure S2: I. Additionally, a tiny quantity of 4b of product was produced when (A) was stirred at room temperature or refluxed in an H2O solution containing barbituric acid (3) without the photocatalyst and visible light (as seen in Figure S2: II, III). In contrast, a small quantity of compound 4b was produced when compound (A) and barbituric acid (3) were combined with 3DPAFIPN and H2O in the absence of visible light (as shown in Figure   S2: IV). In addition, a minuscule amount of 4b was created when compound (A) and barbituric acid (3) were combined with blue light and H2O in the absence of the 3DPAFIPN photocatalyst (as seen in Figure S2: V). The outcomes of the controlled studies showed that 3DPAFIPN and blue LED exposure were both necessary for the advancement of the reactions under consideration.  Figure S2. Control experiments on intermediate A.

3. The reaction mechanism's response to daylight and darkness
The primary goal of the current work is to better understand how visible light and darkness/daylight interact with one another in chemical reaction mechanisms. This investigation examines a number of reactions to assess how darkness and daylight affect the efficacy of H2O (3 mL) and 3DPAFIPN (0.2 mol%). Observations indicate that the emission of this chemical is significantly reduced when observable light wavelengths are disregarded.
The yield (%) obtained for the 4b synthesis under the influence of daylight: trace The yield (%) obtained for the 4b synthesis under the influence of darkness: trace

4. The impact of reaction temperature
To confirm the necessity of visible light radiation for the phase under test, a number of control experiments were carried out using tried and true techniques. To determine the effects of exposure to visible light radiation on the mentioned process, a research investigation was carried out. It has been demonstrated that these reactions can only be brought on by prolonged exposure to light. In the absence of visible light irradiation, low product yields and delayed reaction kinetics were seen. The fact of the matter is that reactions are started by using radiation from visible light sources. As illustrated in Figure S3, blue LEDs, also known as light-emitting diodes, serve as a significant source of visible light energy that is widely applied in many processes.

5. Time's impact on the yield reaction
The inquiry also revealed that the presence of 3DPAFIPN, blue light irradiation, and H2O is necessary to induce the outcomes, confirming them as important factors in determining the successful conclusion of the "investigation". Additionally, it was found that, as shown by the data in Table S1, an increase in reaction time had no discernible impact on the output reaction yield. Regardless of the concurrent usage of 3DPAFIPN, Table 2, Item 2 documents the execution of the chemical reaction in low light. The outcomes of controlled studies demonstrate that, whether or not there is daylight present, the reaction efficiency is minimal in the absence of visible light.